Connecting wires are often used to mechanically and electrically connect a semiconductor chip to a substrate or wiring board. This electrical connection joins the connection surfaces of the semiconductor chip to the strip conductors situated on the substrate/wiring board. For this reason, materials with good electrical conductivity, such as gold, a gold alloy, copper, or a copper alloy, are often used.
Bonding processes are often used for attachment and connection of connecting wires to a substrate or semiconductor chip. Bonding processes (more precisely, wire bonding processes) refer to connection techniques in electrical engineering in which a connection is established between a chip and a wiring board, using a thin wire (connecting wire), and the wire is welded to the connection surface. The welding may be performed, for example, by thermal activation (thermosonic bonding) or by ultrasound (ultrasonic or US bonding), with the advantage that when aluminum wire is used, ultrasonically assisted wire bonding allows a bond connection to be made at room temperature. The electronic elements are thus protected from overheating. A further advantage of US bonding at room temperature is that it is not necessary to heat components having large volumes (and which are thus difficult to heat), thereby reducing manufacturing time and saving energy.
Coated connecting wires represent a refinement of such wires for better utilization in the US bonding process. In this process, core wires made of highly conductive material are coated to assist with US bonding.
Various types of coated connecting wires and bonding processes for same are known. DE 42 32 745 C2 describes a connecting wire which may be attached to a component by ultrasonic bonding. The known connecting wire has a core made of gold or copper, and a coating of aluminum or aluminum oxide which is applied to this core, the coating having an average layer thickness of 5 nm to 100 nm. The connecting wire with the coating allows a secure bond connection at room temperature, in particular for ultrasonic bonding. A current disadvantage of this connecting wire is the reduced service life of the US bonding tool compared to uncoated wire as the result of deposits of coating material on the bonding tool.
The connecting wire known from DE 10 2006 023 167 B3, in which a softer material is provided on a harder core, has the same disadvantages. Here as well, deposits of the coating material on the bonding tool are observed, resulting in reduced tool service life and/or imprecision in the bonding process.
A semiconductor component having a bonding island and a terminal which is connected to the semiconductor chip bonding island via a coated copper connecting wire is known from DE 102 61 436 A1. The coating is an oxidation protective layer composed of palladium or platinum. This technical approach can be used only in the so-called ball bonding process, in which the wire end is melted before a bonding operation in order to form a droplet with better bonding capability. For this purpose, oxidation of the surface must be avoided.
Bonding wire which likewise is usable only by means of a ball or wedge bonding process, as well as manufacture and use thereof, is known from DE 10 2005 011028 A1. A copper connecting wire in which gold is enriched in the surface is disclosed therein.
On the basis of these references, there is a desire to provide a connecting wire which on the one hand allows a high degree of security and reliability in ultrasonic bonding, and on the other hand allows economical and problem-free production of electronic components and assemblies. There is a further desire for connecting wires which may be easily and reliably bonded and which have little or no limitations in functionality as a mechanical and electrical connection.